Schneider Electric 890USE17700 - Manual (Page 162)

Advanced Configuration Features
162 890USE17700 April 2004
Fallback States
for Reflex
Functions Only an output module channel to which the result of a reflex action (See What Is a
Reflex Action?, p. 156) has been mapped can operate in the absence of the NIM’s
heartbeat message.
When modules that provide input for reflex functionality fail or are removed from the
island, the channels that hold the result of those reflex actions go into their fallback
states.
In most cases, an output module that has one of its channels dedicated to a reflex
action will go to its configured fallback state if the module loses communication with
the fieldbus master. The only exception is a two-channel digital output module that
has both of its channels dedicated to reflex actions. In this case, the module may
continue to solve logic after a loss of fieldbus communication. For more information
about reflex actions, refer to the Reflex Actions Reference Guide (890 USE 183).
Configured
Fallback To define a customized fallback strategy for individual modules, you are required to
use the Advantys configuration software. Configuration is done channel by channel.
You can configure a single module’s multiple channels with different fallback
parameters. Configured fallback parameters—implemented only during a
communications failure—are part of the configuration file stored in the NIM’s non-
volatile Flash memory.
Fallback
Parameters You can select either of two fallback modes when configuring output channels with
the Advantys configuration software:
z hold last value—In this mode, outputs retain the last values they were assigned
before the failure.
z
predefined value—In this (default) mode, you can select either of two fallback
values:
z
0 (default)
z
some value in acceptable range
The permissible values for fallback parameters in the predefined value mode for
discrete and analog modules and reflex functions appear in the following table:
Module Type Fallback Parameter Values
discrete 0/off (default)
1/on
analog 0 (default)
not 0 (in range of acceptable analog values)
Note: In an auto-configured system, default fallback parameters and values are
always used.